(CNN) - The liberal group, MoveOn.org, endorsed Democratic Rep. Ed Markey of Massachusetts on Thursday in his bid for the Democratic nomination in his state’s open U.S. Senate race.

According to a survey of its 219,000 members in the Bay State, MoveOn found that 94% voted to endorse Markey, well above its two-thirds threshold for endorsing a candidate. Rep. Stephen Lynch, a social conservative from South Boston, is also running for the Democratic nomination.Follow @politicalticker

Markey, the longest serving member of THE Massachusetts' congressional delegation, has already received wide support from the Democratic establishment in the state and in Washington. The winner of the election will succeed Secretary of State John Kerry, who held the seat until he was confirmed by the Senate earlier this year.

"MoveOn.org members have spoken clearly and decisively for the progressive values that Rep. Ed Markey would support in the Senate," said Ilya Sheyman, Campaigns Director at MoveOn.org. "MoveOn members will put our substantial people power to work, mobilizing volunteers and bundling contributions to ensure Ed Markey is Massachusetts' next Senator."

The group endorsed Elizabeth Warren in her successful attempt to unseat then Sen. Scott Brown, a Republican, last fall. MoveOn members made more than $1 million in small contribution to Warren's campaign and added 750 volunteers to her ranks, according to the group.

On the Republican side, three candidates–Gabriel Gomez, state Rep. Dan Winslow, and former U.S. attorney Michael Sullivan–have jumped in the ring.

Gov. Deval Patrick appointed William "Mo" Cowan, his former chief of staff, to fill the seat as an interim senator until the general election in June.